Electrolytic demetallizing apparatus having electrolyte-pressure-responsive load-compensating means

ABSTRACT

This application discloses an electrolytic demetallizing apparatus adapted to drive a shaping cathode toward and into a conductive metal workpiece, with a gap that is maintained between the cathode and workpiece being filled by pressurized, rapidly flowing electrolyte through which electric current flows between the cathode and workpiece. The apparatus contains drive means for producing relative movement of the cathode and workpiece at a constant rate along a path that determines the shaping of the workpiece. Also, a hydraulic load-compensating means urges the cathode forward into the workpiece to at least partially counteract the tendency of the electrolyte pressure to produce relative retracting movement between the cathode and the workpiece. The load-compensating means is directly responsive to a change of electrolyte pressure between cathode and workpiece, so that the load-compensating force is relieved upon a sudden decrease in the electrolyte pressure such as may be occasioned when the electrode breaks through the workpiece upon completion of the shaping step.

nit-ed States Patent 1151 3,637,481

Williams a 1451 Jan. 25, 1972 [54] ELECTROLYTIC DEMETALLIZING 1,062,5933/1967 Great Britain.. .,..204/l43 APPARATUS HAVING ELECTROLYTE 38/128297/1963 Japan ....204/224 Japan COMPENSATING MEANS Primary Examiner-JohnH, Mack 72 I t I L I Assistant Examiner-D. R. Valentine 1 men or ynn IIams wmnetka At10rneyDressler, Goldsmith, Clement&Gordon [73] Assignee:Anocut Engineering Company 22 Filed: Sept. 24, 1968 [57] ABSTRACT I Thisapplication discloses an electrolytic demetallizing ap- [211 Appl'762077 paratus adapted to drive a shaping cathode toward and into aRelated s Application Data conductive metal workpiece, with a gap thatis maintained I between the cathode and workpiece being filled by preslcontlnuatlon-m-part of Sara 6, surized, rapidly flowing electrolytethrough which electric cur- 1967, abandonedrent flows between thecathode and workpiece. The apparatus contains drive means for producingrelative movement of the [52] U.S. Cl ..204/224, 204/ 143 M, 204/225 h dand workpiece at a constant rate along a path that 3 1! 2, 3p Udetermines the shaping of the workpiece. Also, a hydraulic Field ofSearch 143 load-compensating means urges the cathode forward into theworkpiece to at least partially counteract the tendency of theReferences cued electrolyte pressure to produce relative retractingmovement between the cathode and the workpiece. The load-compensat-UNITED STATES PATENTS ing means is directly responsive to a change ofelectrolyte 3,365,381 l/l968 Fromson ..204 229 x Pressure betweenCathode and workpiece, so that the load- 3,399,125 8/1968 Mikoshiba etal ..204 224 x compensating fem is relieved upon a Sudden decrease inthe 2 4 2 X electrolyte pressure such as may be occasioned when theelec- 20 trode breaks through the workpiece upon completion of the3,409,535 11/1968 Rossetal 3,433,727 3/1969 Keelevic...

3,475,303 10/1969 Sadler et al. ..204/224 x Shaping Step- FORElGNPATENTS OR APPLICATIONS 9 Claims, 7 Drawing Figures 1,029,233 5/1966Great Britain 1.204/224 ELECTROLYTIC DEMETALLIZING APPARATUS HAVINGELECTROLYTE-PRESSURE-RESPONSIVE LOAD-COMPENSATING MEANS CROSS-REFERENCETO RELATED APPLICATION BACKGROUND OF THE INVENTION Field of theInvention Electrolytic demetallizing is a now well-known processinvolving the removal of metal from an anodic workpiece by maintaining astream of electrolyte between the workpiece and a shaping cathode whichis not in mechanical contact with the workpiece, while passing directcurrent therebetween through the stream of liquid electrolyte. See, forexample, US. Pat. Nos-3,058,895 and 3,130,140.

Electrolytic demetallizing can be used to sink cavities and to produceshapes in metal, including hard alloys which are machined conventionallywith the utmost difficulty.

OPPOSING FORCE FROM HIGH ELECTROLYTE PRESSURE The best results areobtained in the electrolytic demetallizing process when the workpiece isspaced only a very short distance from the shaping cathode, andelectrolyte flows through the gap between workpiece and cathode at ahigh velocity and relatively high pressure, frequently 200 p.s.i. orabove.

In the use of cathodes of large cross-sectional area, the hydrostaticforce tending to push the cathode away from the work becomes quitelarge. If, for example, the effective crosssectional area of the cathodeis, say, 100 square inch, and if the effective hydrostatic pressure ofelectrolyte between the cathode and the workpiece is, say 200 p.s.i.,then the total force rises toward 20,000 lbs., the exact value beingdependent upon the extent of the Bernoulli effect and the consequentstatic pressure in the work gap. The mechanism required to move thecathode toward the workpiece against the force in a smooth and uniformmanner is heavy and expensive. Also, it becomes extremely difficult tomove the cathodes at a uniform rate of advance against such high backpressures, although a uniform rate of advance is generally important forthe erosion of uniformly shaped cavities.

NEED FOR PROMPT SHUTOFF OF LOAD- COMPENSATING MEANS It is also known toprovide an additional load-compensating means for an electrolyticdemetallizing apparatus having a cathode of large cross-sectional areathat is subject to strong reaction forces as justdescribed.

While the known load-compensating means, such as a hydraulic systemarranged to augment the drive system in accordance with the actualelectrolyte pressure, successfully assists the drive means in providinga steady advance of the cathode by partially compensating for thehydrostatic force opposing such advance of the cathode, a problem arisesat the point where the cathode fully penetrates the workpiece and breaksthrough the back surface. The electrolyte pressure between cathode andworkpiece immediately drops, suddenly reducing the opposing reactionforce on the cathode. If the load-compensating means is not deactivatedimmediately when the electrolyte pressure falls, the continued forwardforce applied by the load-compensating means will cause the cathode toimpact with the workpiece, causing damage to both.

ADVANTAGES OF THE INVENTION This invention provides electrolyticdemetallizing apparatus which is particularly suitable for use withshaping cathodes of large cross-sectional area, against which opposingreaction forces of up to l0 tons or more can be developed by thepressurized electrolyte without the above-stated undesirable effectstaking place.

The apparatus of this invention canbe used to erode large cavities inmetal workpieces, and upon a sudden drop in in electrolyte pressure,caused for example, by a breakthrough at the back of the workpiece, thecathode does not surge forward into contact with the workpiece and thusdoes not damage the cathode or workpiece.

SUMMARY OF THE INVENTION This application relates to an electrolyticmachining apparatus which contains means for mounting a shaping cathodein predetermined position with respect to a conductive metal workpieceto define a gap therebetween, means for flowing electrolyte between thecathode and the workpiece and through said gap under positive pressure,the electrolyte pressure tending to produce relative retraction betweenthe cathode and the workpiece, and means for controlling relativemovement between the cathode and the workpiece to maintain apredetermined gap in the presence of the electrolyte pressure, saidlast-named means including drive means for producing relative movementof the cathode and workpiece along a path that determines the shaping ofthe workpiece, load-compensating means for at least partially opposingsaid tendency to relative retraction between the cathode and theworkpiece, and means connected in load-controlling relation to saidcompensating means and directly responsive to electrolyte pressurebetween the cathode and the workpiece for relieving theload-compensating means upon a sudden decrease in said electrolytepressure.

THE DRAWINGS In the drawings:

FIG. 1 is a diagrammatic lengthwise section showing one embodiment ofthe apparatus of this invention in the operation of eroding acylindrical hole through a conductive metal workpiece.

FIG. 2 is a diagrammatic lengthwise section showing another embodimentof the apparatus of this invention in the same operation of eroding acylindrical hole through a conductive metal workpiece.

FIG. 3 is a sectional view taken along a vertical plane passing throughanother embodiment of the apparatus of this invention.

FIG. 4 is a sectional view, taken along line 4-4 of FIG. 3, of the sameapparatus.

FIG. 5 shows a modification of a portion of the apparatus of FIGS. 3 and4, taken in section along a vertical plane.

FIG. 6 is a sectional view taken along line 6-6 of FIG. 5.

FIG. 7 is a partial view taken along line 77 of FIG. 5.

DESCRIPTION OF SPECIFIC EMBODIMENTS Referring to FIG. 1, a hollow,cylindrical-shaping electrode 2 is carried by a hollow holder 4 to beadvanced toward a conductive metal workpiece 6 to form a narrow gaptherebetween.

A pressurized liquid electrolyte supply system for maintaining a streamof electrolyte flowing across the gap includes an electrolyte storagecontainer 8, a feedline 9 equipped with a pressure pump P, and aslidable feed bushing 10. The feed bushing 10 serves as a guide cylinderfor the electrode holder or mounting means 4 and is adapted to engage insealing relation against the workpiece and provide an annular flow spacethat surrounds the gap and confines the electrolyte against escape. Areturn line 12 for the electrolyte leads from the holder 4 to completethe primary electrolyte flow path. This path is shown to lead reverselythrough the electrode and electrode holder, i.e., from outside theelectrode through the work gap between the electrode and the workpieceand then into the interior of the electrode.

The slidable feed bushing may be of any suitable electrically insulatingmaterial. It houses the holder 4 and cathode 2 in a relationship topermit electrolyte pressure to cause the bushing to be held in sealedengagement against the workpiece 6.

The feed mechanism for advancing the electrode and electrode holder isdesignated generally at 14 and includes adapter plates 16, 17, plate 16being of any suitable electrically insulating material connected inthrust-transmitting relation to the rear end of the electrode holder 4.If the electrode cathode assembly is large, there will be a high forceagainst advance of the cathode. The drive system may then be augmentedby a load-compensating means to be described below that is capable ofproducing a strong additional forward thrust.

Variations in electrolyte pressure at the gap region, whether caused byvariation in the supply pressure or by other environmental changes inthe electrolyte flow system, impose transient demands upon the drivesystem that could, in the absence at such a load-compensating means,lead to erratic advance of the electrode 2. In the most extremesituation, when the electrode bores through the bottom face of theworkpiece 6 and allows direct escape of electrolyte, the effectiveelectrolyte pressure at the gap region falls abruptly, and theload-compensating means, no longer balanced by the electrolyte reactionforce, tends to push the electrode against the workpiece by driving itforward with sudden surge which is independent of the slow forwardmotion caused by the drive means. This happens because the electrodeusually breaks through the bottom of the workpiece at a localized regionso that the hole is not full size to permit the electrode to passthrough without touching the workpiece. Typically, the normal gapclearance between the electrode and the workpiece is small, and uponrelease of the electrolyte pressure at the gap, the resilience of thedrive mechanism, and the play in the drive parts, allows the electrodeto jump forward into damaging contact with the workpiece when urged bythe load-compensating means.

In the drive system, there is shown a main guide housing 19 of elongatedcylindrical open-ended form, a ram 19 slidably mounted therein andprojecting through the open end thereof, and an enlarged ram head 20carried externally on the ram and secured to the adapter plate 17. Themain housing 18 is fitted with a sleeve bushing 21 within its open endfor slidable guiding engagement with the ram shaft 19 and housing 18 isalso fitted with a radial bearing 22 and an intermediate thrust bearing23 rotatably mounting the end and intermediate journal portions of adrivescrew 24. A collapsible protective boot 25 of bellows form isanchored between the ram head 20 and the guide housing 18 to enclose andprotect the exposed portion of the ram shaft 19. The ram shaft 19 has astepped diameter axial bore 198 forming a mounting socket for a drivenut 26 that cooperates with the drivescrew to advance and retract theram head 20.

A drive motor 27 is shown with a shaft 275 carrying a sprocket 28 fordriving a sprocket 29 on the drivescrew shaft. A suitable link chain 30is shown trained about the sprockets 28, 29 and an electric brake 31 isshown within the guide housing 18 to engage the extreme end of the driveshaft.

In normal operation, the motor 27 drives the ram head 20 to advance itat a constant rate of speed during machining operations, or to retractit, the drive being from the sprocket 28, through the chain 30 to thesprocket 29 to rotate the drivescrew 24. The drive nut 26 is fixedwithin the ram shaft to control the ram shaft 19 in accordance with thespeed and direction of rotation of the drivescrew.

Electrolyte is supplied through the feedline 9 to the feed bushing 10and flows across the gap between the workpiece 6 and the electrode 2,and then through the electrode 2 and holder 4 to the return line 12. Theelectrolyte pressure at the gap and acting on the differential areapresented by the electrode and electrode holder is determined by thepump P and typically may be about 250-200 p.s.i. A direct current powersource is represented at 32 and is shown connected to the workpiece 6and the electrode holder 4 in a sense to make the workpiece anodic andthe shaping electrode cathodic.

As described thus far, the shaping cathode is arranged to sink a hole inthe workpiece. Current flow across the electrolyte gap between theshaping cathode and the workpiece removes metal from the workpiece asthe drive system advances the electrode. It is desirable that the drivesystem not be subjected to the high-opposing reaction force which may bepresent with large work areas. It is also desirable that the drivesystem be capable of adapting to rapid changes in electrolyte pressureto prevent surges in the movement of the drive system.

In accordance with the present invention, a load-compensating system isassociated with the ram head 20 to develop hydrostatic forces assistingadvance of the ram head to at least partially counteract the reactionforce occasioned by the highpressure electrolyte acting at the gapregion. A balanced array of hydraulic piston and cylinder mechanismseach designated generally at 33 is shown connected directly to the ramhead 20 to assist its advance. Each mechanism, as shown for purposes ofillustrative disclosure, has a single ended piston 34 and piston rod 35in rigid driving engagement with the ram head 20 and a cylinder 36housing the piston and defining a pressure chamber 37 therefor.

Hydraulic pressure is applied to the pressure chamber 37 to produce acompensating force proportional to the reaction force. The relationshipsof pressure and area in the hydraulic mechanisms 33 are generallyselected to partially compensate for the reaction force caused bypressurized electrolyte in the gap region so that the drive system issubjected to a reduced unbalanced reaction force resulting fromelectrolyte pressure.

In the particular arrangement disclosed herein, the electrolyte feedsystem has a branch line 38 leading from the discharge side of the pumpP and connected to the pressure chambers 37 to utilize electrolyte atthe actual feed system pressure as the actuating medium for thehydraulic compensators 33. Any changes in the electrolyte pressure occursubstantially simultaneously at the gap region and in the compensatingchambers 37, so that such changes automatically cancel out and do notpresent surge conditions to the drive. For example, when the shapingelectrode 2 breaks out through the rear face of the workpiece, the closeclearance gap conditions and the through flow electrolyte path aredisrupted and there is a sudden drop in pressure at the gap region witha consequent sudden drop in the electrolyte reaction force on the ramhead 20. This drop in electrolyte pressure is immediately reflected in aloss of pressure at the discharge side of the pump P so that thepressure acting in the chambers 37 of the hydraulic mechanisms alsodrops proportionately, to maintain the desired balance of forces at theram head and thereby prevent contact with the workpiece. Other changesin system pressures due to variation in pump output pressure or forother reasons are reflected rapidly between these regions to maintainthe desired balance and allow the drive system to determine and maintaina uniform and steady advancing movement of the electrode.

Another embodiment of the invention is shown in FIG. 2 for producing acompensating force that partially counteracts the reaction forceoccasioned by the electrolyte pressure acting on the area presented bythe electrode and holder assembly. Corresponding reference characters inthe series are used to identify corresponding parts.

Accordingly, in FIG. 2, a hollow-shaping electrode 102 is carried by ahollow holder [04 to be advanced toward a conductive workpiece 106 tomaintain a narrow gap therebetween. A pressurized liquid electrolytesupply system for maintaining electrolyte flow at the gap includes astorage container 108, a feedline I09 equipped with a pressure pump Pand leading into the upper end of the electrode holder 104. A splashshield 110 is shown contacting the workpiece I06 and encircling theholder 104 to accommodate relative advancing and retracting movement ofthe electrode and holder assembly. A return line 112 is shown leadingfrom the splash shield 110 to complete the electrolyte flow path which,in this embodiment, is shown to extend forwardly through the holder 104and the electrode 102, then out of the electrode and through the workgap between the electrode and the workpiece.

The drive mechanism for the electrode assembly, designated generally at114, includes a pair of adapter plates 116, 117, the plate 116 being ofany suitable electrically insulating material mounted in thrust relationto the end of the holder 104. In this system, the differentialareaexposed to electrolyte pressure by the electrode assembly again resultsin a high opposing reaction force action to resist steady advance of theelectrode by the drive mechanism toward the workpiece. A typicalload-compensating system vis shown herein to partially balance out theseelectrolyte reaction forces and allow the drive system to effect auniform advance of the electrode. However, variations inelectrolytepressure at the gap region, whether caused by supply pressurevariations or by breakthrough of the electrode through the workpiece orby other environmental changes in the electrolyte flow, impose transientdemands upon the drive 114 leading to erratic advance of the electrodeunless the load-compensating system instantaneously balances suchvariations. 1

In the drive system disclosed in FIG. .2, there is shown a main guidehousing 118 (represented 'only fragmentally) and a ram 119 shiftablymounted therein. Ram 119 includes a ramhead 120 projecting through thelower end thereof, and is guided by antifriction-bearing elements 121mounted within the guide housing 118. A drivescrew 124 engages a drivenut 126 carried in the upper end of the ram, the upper end of thedrivescrew being shown projecting through a thrust bearing 123 shownmounted on a frame structure 123F.

A drive motor 127 is shown powering a variable speed drive 127V and agear-reducer unit 127R to rotate a drivesprocket 128 for powering asprocket 129 by means of a link chain 130. The sprocket 129 is mounteddirectly on the upper end ofthe drivescrew 124.

The load-compensating system 115 includes a pair of hydraulic mechanisms133 each of which comprises a singleended piston 134 and piston rod 135that is in rigid driving engagement with the ramhead 120, and a cylinder136 housing the piston and defining a pressure-chamber 137 therefor.Hydraulic pressure is applied to the pressure chambers 137 through afcedline 138 from a recycling hydraulic fluid system 139, the feedline138 being shown with a supply valve 140.

The hydraulic recycling system 139 includes a storage tank 141, adischarge line 142 leading from the bottom of the tank 141 and equippedwith a hydraulic fluid pressure pump P and a return line 143 leading tothe storage tank and equipped with an adjustable pressure-regulatingvalve 144. Thus, the pressure maintained in the recycling system isselectively adjustable to provide control of the pressure .acting on thepistons 134 .and thereby acting to assist advance of theram head 120.Typically, the pressure and area relationships established in thecompensating system 115 provide a compensating force to partiallyneutralize the opposing reaction force caused by pressurized electrolytein the gap region. Thus, the load seen by the drive is limited to arange at which the drive system can produce a uniform advance of theelectrode. Exact balance between the reaction force and the compensatingforce is not necessary so long as the load on the drive system is notexcessive.

In the disclosed arrangement, the drive system load is monitored,and-automatic adjustment of the hydraulic pressure is effected tomaintain the drive system load within a prescribed range. For thispurpose, a strain gauge 145 of any suitable type is mounted upon atransverse support arm 123A of the frame 1231* to sense bending strainproduced on the arm I23A'by the effective drive system load. The straingauge controlsthe operation of an amplifier 146 which governs thesetting of the adjustable pressure-regulating valve 144.

When the bending strain sensed by the gauge 145 rises due to anincreased electrolyte back pressure,'the amplifier 146 progressivelythrottles the valve 144 to increase the pressure in thehydraulic-recycling system and correspondingly to increase thecompensating force applied through the piston rods 135. When the bendingstrain dropsbelow a predetennined minimum valve, indicative ofovercompensation, the gauge 145 signals the amplifier 146 to open thevalve 144 to effect a reduction of pressure in the hydraulic-recyclingsystem and allow the drive system to accept its normal load.

A .direct current power source is represented at 132 and is shownconnected to the workpiece 106 and the electrode holder 104 in a senseto make the workpiece anodic and the exposed endface of the electrodecathodic.

In the general operation of the system, current flow is main tainedthrough the pressurized electrolyte at the gap to erode the workpiece asthe cavity-sinking electrode 102 advances. During this action, thehigh-reactionforces associated with the high-electrolyte pressuresrequired for efficient demetallizing are partially balanced by thecompensating force applied through the hydraulic mechanisms 133.Continuous control over .the compensating action is efiected by thestrain gaugel45 and amplifier 146.

While the described system is effective for maintaining a steady advanceof the electrode in the presence of minor or gradual variations inelectrolyte pressure, sudden and significant pressure drops require amore rapid compensating system response. When the electrode breaksthrough the remote face of the workpiece, a sudden drop in theelectrolyte back pressure results due to the interruption of theelectrolyte throughflow path. The compensating force would immediatelypredominate and push the electrode against the workpiece to the damageof both parts, before an adjusting response through the strain gauge,amplifier andpressure valve system could occur.

In accordance with the present invention, sudden drops in electrolytepressure are directly sensed, and controls are provided for directly andrapidly reducing the hydraulic pressure acting .in the compensatingsystem. For this purpose, a pressure-sensitive transducer such aspiezoelectric element 147 (protected, of course, from corrosion byelectrolyte) is mounted within the electrode holder 104 upstream of thegap to be exposed to the electrolyte pressure in the stream ofelectrolyte flowing to the gap and to produce a control signalproportional to such pressure. The hydraulic-compensating system hasexhaust lines 148 leading from the cylinders 136 and equipped withpressure relief valves 149. Control signals from the transducer 147 areapplied through a control circuit 150'adapted to pass rapid signalchanges but not slow signal changes. Control circuit 150 is connected bycontrol wires 15l.to effect rapid opening of relief valves 149, inresponse to a rapid signal change from transducer 147, to relievehydraulicpressure from the load-compensating system immediately uponsudden loss of electrolyte pressure at the transducer.

The relief of hydraulic pressure precludes any sudden forward thrust ofthe electrode, thereby preventing damaging impact with the workpiece.The sudden loss of pressure due to workpiece breakthrough usually occursbefore the cavity is completely cleared of workpiece material. Upon lossof electrolyte pressure, thedrive balance is restored by immediatelyrelieving the hydraulic pressure on the compensating system, andthe'main drive system 114 continues its steady advance of the electrodeaccompanied by final erosion of the workpiece, all without any contactwith the workpiece.

FIGS. 3 and -4 disclose another embodiment of the apparatus ofthisinvention, which has a large electrode capable of beingmoved byadrive mechanism into a workpiece at a uniform rate of advance, and whichalso has load-compensating means for partially neutralizing theretroactive force generated by pressurized electrolyte located betweentheelectrode and the workpiece. The load-compensating means comprises achamberat the rear of the electrode into which pressurized fluid can beadmitted to pressurize the back of the electrode, providingload-compensatingforce to neutralize a portion of the retractive force.

Electrode 201 is shown to be a large plate having a threedimensionalcontour to its bottom surface. This type of electrode is typically usedto prepare large dies having a contour to their working surface of shapegenerally complementary to the contour of the lower surface of theparticular electrode used.

Electrode 201 is shown in adjacent relation with workpiece 203 which isshown already shaped by electrode 201 through operation of theapparatus. The workpiece rests on table 204, and is surrounded byinsulating spacer 205, which has a central space in which the workpiececlosely fits. Spacer 205, in turn, abuts against wall 207 which servesas a position-locating means for the workpiece along one horizontalaxis, while one or more pins 208 (seen in FIG. 4) serve to locate theworkpiece along a second horizontal axis. Thus, workpiece 203 can beprecisely positioned under the electrode by simply abutting it againstwall 207 and pins 208.

Sockets 210 are used to hold pins 208. Only one socket 210 is shown inuse, the remaining sockets being put to use when it is desired toposition a workpiece of different size or to position a workpiece at adifferent location.

In the embodiment shown, the workpiece is sufficiently large and heavyso that no means for positively holding it in one position is required.

Table 204 carries conventional airlift devices 211 to facilitate thesliding of workpiece 203 on and off table 204.

Electrode 201 is held by adapter plate 212, which, in turn, is carriedby electrode mount 213, to constitute a cathode member. Apertured plate214 is held between plate 212 and mount 213. Mount 213 is stiffened andrendered inflexible by a plurality of vertical fins 215 which extendfrom the mount 213 to push rod 217, which is shown to be an integralpart of mount 213. The horizontal area of push rod 217 is substantiallyless than the horizontal area of mount 213 for a reason explained below.

A ramhead 219 is affixed to the top of push rod 217, and ram head 219 isin turn affixed to a conventional ram (not shown), which is typicallyoperated in the manner of FIGS. 1 or 2 by a drivescrew, a thrustbearing, and a motor to provide a uniform rate of advance of theelectrode 201 toward the workpiece 203 during electrochemical machining.

While only one push rod 217 is shown in this embodiment, it iscontemplated that a plurality of push rods can be used in this inventionto engage electrode mount 213 so that the electrode can be advanced witha minimum of bending due to electrolyte back pressure. A plurality ofpush rods would desirably be used in cases where electrode 201 and mount213 are of exceptionally large area.

Cover 221 surrounds push rod 217 and is affixed to wall 207 and othersupports 223, typically by bolts, to define a pressure chamber 225 incooperation with the back side 226 of electrode mount 213. Stressmembers 222 limit bulging of the cover when chamber 225 is heavilypressurized. Push rod 217 extends through an aperture in the top ofcover 221 in sliding relation thereto to permit push rod 217, mount 213,and electrode 201 to be raised and lowered with respect to cover 221 andthe workpiece 203.

Plungers 227 can be inserted into recesses 229 in push rod 217 to holdthe push rod 217 and cover 221 together. The cover 221 can then beunbolted from wall 207 and supports 223, and the push rod and cover canbe raised together to obtain access to the workpiece 203.

In the embodiment shown in FIGS. 3 and 4, pressurized electrolyte is fedthrough inlets 231, passing through the region 233 between electrode 201and insulating spacer 205, and from there passing to work gap 235between electrode 201 and workpiece 203. The pressurized electrolyte isdrained from the work gap 235 by electrolyte flow channels whichcomprise slots 236, some of which lead into chambers 237. Theelectrolyte passes into slots 236, through electrode 201, and intohorizontal channels 239 (best seen in FIG. 4) in the adapter plate 212.Channels 239 are closed at their ends.

The pressurized electrolyte passes along horizontal channels 239 to apoint underneath an aperture 219 in plate 214. The electrolyte thenflows through apertures 216 into one of a plurality of radial channels241, formed in the interior of electrode mount 213, and which pass overhorizontal channels 239. The electrolyte then passes from radialchannels 241 into vertical channels 243 in push rod 217 and out of thedevice by exit ports 245. In the disclosed embodiment, eight radialchannels 241 diverge in an equiangular manner out from push rod 217 topass over horizontal channels 239.

If desired, the apertures 216 in plate 214 can be so arranged thatelectrolyte flowing into slots 236 in high areas 255 of electrode 201(see FIG. 3) is transported to different radial channels 241 andvertical channels 243 than the electrolyte flowing into slots 236 whichare located in low areas 257 of the electrode.

The advantage of this is that the channels 243 which carry electrolytefrom slots 236 located in low areas 257 of the electrode can then beblocked to prevent the flow of electrolyte during the initial stage ofelectrolytic machining, before the workpiece has substantially assumedthe configuration of the working face of the electrode.

The reason that this is desirable is that, in the initial stage, highareas 255 are in close proximity with the workpiece 203, but low areas257 are not, leaving wide spaces at various places between the electrodeand the workpiece. Depending upon the configuration of the electrode, itis possible that wide channels between the electrode and the workpiececan become accessible to the electrolyte to permit it to flow throughthe electrode and out of the apparatus without being forced under highpressure between the narrow work gap 235, which at this point existsonly in the vicinity of high areas 255. This can cause the electrolytepressure to drop substantially, interfering with the operation of theapparatus.

To counteract this, the above modification can be used in conjunctionwith valves to close those vertical channels 243 which connect withslots 236 in the low areas 257 of the electrode, to prevent the flow ofelectrolyte therethrough. After sufficient electrolytic demetallizationhas taken place in the vicinity of high areas 255 to cause the workpieceto assume the general configuration of electrode 201, the valves areopened to permit electrolyte to flow through slots 236 in low areas 257.Electrolytic demetallization then takes place uniformly over the entireworking face of the electrode.

Pressurized electrolyte which is passed into the apparatus by inlets 231also passes into pressure chamber 225 via the passage 246 definedbetween the periphery of adapter plate 212 and electrode mount 213, andcover 221. Pressurized electrolyte is prevented from escaping chamber225 between push rod 217 and the wall of the aperture in cover 221through which rod 217 passes by annular seal 247. Seal 247 is carried bycover 221 and surrounds push rod 217, providing a pressure seal throughwhich the push rod can slide. A seal to prevent the escape ofelectrolyte can also be placed between the bottom of cover 221 andinsulating spacer 205.

Thus, as pressurized electrolyte is provided to the work gap 235 topermit the flow of electric current between electrode 201 and workpiece203 for demetallizing and shaping the workpiece, pressurized electrolytealso flows into chamber 225. The back pressure against electrode 201which is created by pressurized electrolyte in work gap 235 is thuspartially neutralized by a forward pressure exerted on back 226 of theelectrode mount 213 by pressurized electrolyte in chamber 225. Theresulting back pressure which is sensed by push rod 217 and the drivemeans for the rod is theoretically the product of the mean pressure ofthe electrolyte in work gap 235 multiplied by the transverse area ofpush rod 217, since the back pressure of electrolyte in work gap 235against the remaining area of electrode 201 and the other parts exposedto electrolyte back pressure is counterbalanced by the electrolytepressure on back 226 of the electrode mount.

In the event of a change in electrolyte pressure in the system, caused,for example, by a failing or shutting off of the pump sued to providepressurized electrolyte, the drop in electrolyte pressure at the workgap 235 and chamber 225 takes place in an essentially simultaneousmanner, since there is an electrolyte conduit permitting free flow ofelectrolyte between the two regions. Thus the danger that a drop inpressure at the work gap may cause the load-compensating means tooverbalance the system and drive the electrode 201 into damaging contactwith workpiece 203 is essentially eliminated.

Direct electric current passes through the apparatus in a sense to makeelectrode 201 cathodic with respect to workpiece 203. Cables 249 and 251(shown in FIG. 4) connected the apparatus with a source of electriccurrent. The current passes between the cables by way of table 204.workpiece 203, work gap 235 through which pressurized electrolytepasses, electrode 201, plates 212 and 214, mount 213, push rod 217, andram head 219.

The underside of table 204 is shown to be covered with an insulating pad253 to prevent short circuits, and the top of ram head 219 typicallycontains a similar insulating pad (not shown) to prevent the passage ofelectric current into the ram and drive means. Other insulating membersare spacer 205, wall 207, and supports 223, which prevent the directflow of electric current between table 204 and cover 221, limiting thecurrent flow path to travel through workpiece 203 and work gap 235. Theinsulating members used herein can typically be made of composites ofepoxy resin and glass fiber.

Another embodiment of this invention is shown in FIGS. 5 through 7. Thebasic plan and function of the apparatus shown therein is similar to theapparatus of FIGS. 3 and 4, except that the electrolyte flow path issomewhat different. Corresponding reference characters is the 300 seriesare used to identify corresponding parts.

Electrode 301 is shown in adjacent relation to workpiece 303, which isshown in an advanced stage of electrolytic machining, wherein the uppersurface of workpiece 303 conforms to the lower surface of electrode 301.workpiece 303 rests upon table 304, and the workpiece is surrounded byinsulating spacer 305.

Electrode 301 is held by adapter plate 312 to electrode mount 313, withapertured plate 314 mounted between them. Mount 313 is carried by pushrod 317, which extends through an aperture (not shown) in cover 321 todefine a pressure chamber 325. As in the embodiment of FIGS. 3 and 4,pressurized electrolyte is permitted to flow into pressure chamber 325to press against the back 326 of electrode mount 313 to partiallyneutralize the retractive force created by pressurized electrolyte atthe work gap 335 between electrode 301 and workpiece 303.

Pressurized electrolyte enters the apparatus of FIGS. 5 through 7 atinlet 331 to pass into chamber 325 and also to pass horizontally abovespacer 305 into the loop-shaped passage 346 between adapter plate 312and cover 321. Electrolyte also passes into the outer portions of workgap 335.

The electrode of this embodiment has alternating slots 336a and b andoutlets 337, while the adapter plate 312 has alternating horizontalchannels 339a and 12. Channels 33% only lead under apertures 316 inplate 314 to permit flow of electrolyte between each horizontal channel33% and a radial channel 341, which, in turn, leads into a verticalchannel 343. There is no aperture connecting channels 339a with radialchannels 341.

As described above, the apparatus of FIGS. 5 and 6 is quite similar tothe apparatus of FIGS. 3 and 4, differing primarily in the arrangementof apertures 316 in plate 314. A major difference between this and theprevious embodiment is that horizontal channels 339a in this embodimentpass through the sidewall of adapter plate 312 to define'electrolyteentry ports 344 (shown in FIG. 6) for receiving pressurized electrolytewhich occupies the passage 346 (shown in FIG. 5) between adapter plate312 and cover 321. The pressurized electrolyte flows into the horizontalchannels 339a from entry ports 344, the electrolyte flowing alongchannels 339a and then downwardly and out slots 3360 into the work gap335. The slots 336a thus constitute electrolyte inlet channels.

The electrolyte then migrates along the work gap 335 to a slot 336b inthe electrode which serves as an outlet channel for the electrolyte fromthe work gap. The electrolyte passes upwardly through these slots,through chambers 337, to one of horizontal channels 33%, along which itpasses until it encounters an aperture 316 in plate 314, flowing throughthe aperture into a radial channel 341. From there it flows into avertical channel 343 and out of the apparatus.

Thus, this embodiment of the apparatus provides an electrolyticmachining apparatus in which the electrolyte is both fed into andremoved from the work gap by electrolyte chan nels which lead throughthe electrode. An advantage of this is that electrolyte is provided towork gap 335 at points distributed across the face of electrode 301,rather than only at the periphery as in the embodiment of FIGS. 3 and 4.This reduces the possibility of an electrolyte shortage at the center ofthe work gap 335.

In another embodiment of the apparatus of this invention, insulatingspacer 305 can be modified to tightly fit against the side of electrode301, to prevent fluid flow between inlets 331 and work gap 335.Electrolyte entry ports 344 are also sealed. The apertures 316 in plate314 can be so arranged in conjunction with radial channels 341 andhorizontal channels 339 that electrolyte can be pumped down some of thevertical channels 343 (shown in FIG. 6) to pass out some of the slots336 in the electrode, passing across work gap 335 to be collected inother slots 336. The electrolyte then passes into other horizontalchannels 339, radial channels 341, 'and vertical channels 343, and outof the apparatus.

Two separate pressurized fluid systems are used in this particularembodiment, one consisting of pressurized electrolyte flowing to andfrom the work gap 335 via separate vertical channels 343 in the push rod317, and the other system consisting of electrolyte or another fluidpassing through inlet 331 into chamber 325 to provideload-compensatingforce to the back 326 of the electrode.

In this embodiment, a separate control system is generally required torapidly cut ofi the pressure of the fluid in chamber 325 upon a drop inthe pressure of the electrolyte at work gap 335 in order to preventelectrode 301 from moving forward into damaging contact with workpiece303 upon a drop in electrolyte pressure at the work gap 335. This can beaccomplished through the use of a valve in cover 321 connected to apressure-sensing means, similar to the arrangement shown in FIG. 2. Fromthe foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the true spirit andscope of the novel concept of the invention. It is, of course, intendedto cover by the appended claims all such modifications as fall withinthe scope of the claim.

What is claimed is:

1. In electrolytic machining apparatus, mounting means for locating ashaping cathode in predetermined position with respect to a conductivemetal workpiece to define a gap therebetween; means for flowingelectrolyte between the cathode and the workpiece and through said gapunder positive pressure, the electrolyte pressure tending to producerelative retraction between the cathode and the workpiece, drive meansconnected to said mounting means for producing relative movement of thecathode toward the workpiece in the presence of the electrolytepressure; and load compensating means cooperating with said drive meansand separate and spaced from said mounting means for at least partiallyopposing said tendency to relative retraction and responsive to saidelectrolyte pressure, to be rendered inactive upon loss of saidelectrolyte pressure.

2. In electrolytic machining apparatus, mounting means for locating ashaping cathode in predetermined position with respect to a conductivemetal workpiece to define a gap therebetween, means for flowingelectrolyte between the cathode and the workpiece and through said gapunder positive pressure; the electrolyte pressure tending to producerelative retraction between the cathode and the workpiece; drive meansfor causing relative movement of the cathode toward the workpiece alonga path that determines the shaping of the workpiece and in the presenceof the electrolyte pressure; load-compensating means for providingopposing force to counteract at least a portion of the force tending tocause relative retraction between the cathode and the workpiece; saidload compensating means being separate and spaced from said mountingmeans; and means connected in load controlling relation to saidcompensating means directly responsive to electrolyte pressure betweenthe cathode and the workpiece for actuating said low compensating meansin response to elevated electrolyte pressure and for relieving the loadcompensating means upon a decrease in said electrolyte pressure.

3. ln electrolytic machining apparatus, mounting means for locating ashaping cathode in predetermined position with respect to a conductivemetal workpiece to define a gap therebetween; means for flowingelectrolyte between the cathode and the workpiece and through said gapunder positive pressure, the electrolyte pressure tending to producerelative retraction between the cathode and the workpiece; drive meansfor moving the cathode toward the workpiece in the presence of theelectrolyte pressure; load-compensating means for at least partiallyopposing said tendency to relative retraction between the cathode andthe workpiece, and means connected in load-controlling relation to saidcompensating means and directly responsive to electrolyte pressurebetween the cathode and the workpiece for rapidly relieving theloadcompensating means upon a sudden decrease in said electrolytepressure.

4. ln electrolytic machining apparatus, mounting means for locating ashaping cathode in predetermined position with respect to a conductivemetal workpiece to define a gap thercbetween; means for flowingelectrolyte between the cathode and the workpiece and through said gapunder positive pressure, the electrolyte pressure tending to producerelative retraction between the cathode and the workpiece; drive meansfor producing relative movement between the cathode and the workpiece inthe presence of the electrolyte pressure; load-compensating meansresponsive to said tendency to relative retraction to at least partiallyoppose the same; said loadcompensating means comprising at least onepiston and cylinder mechanism interposed between relatively movableelements of said drive means and means for directing pressured fluid tosaid cylinder.

5. ln electrolytic cavity-sinking apparatus, a hollow, electricallyconductive electrode adapted to be advanced toward and into anelectrically conductive and electrochemically erodable workpiece toestablish a work gap for flow of highpressure electrolyte to supportelectrolytic current flow between said workpiece and said electrode;means for establishing an electrolyte flow path passing through saidelectrode and having said gap located intermediately therein; means forflowing electrolyte under positive pressure through said path, theelectrolyte pressure between the cathode and workpiece tending toproduce relative retraction movement between the cathode and theworkpiece; means for passing low voltage, high-density direct currentbetween the cathode and the workpiece in a sense to make the workpieceanodic, and drive means for producing relative movement between thecathode and the workpiece in the presence of the electrolyte pressure,the improvement of load-compensating means for opposing reacting againstsaid drive means due to electrolyte pressure along said path, saidload-compensating means being spaced from said electrode and connectedto said drive means, said load-compensating means being directlyresponsive to electrolyte pressure between the cathode and the workpieceand rendering the load-compensating means inactive upon sudden escape ofelectrolyte from said path at the region of said gap.

6. The apparatus of claim 5 wherein said load-compensating means ishydraulic and includes piston means operable in cylinder means to definea pressure chamber communicating with said path to be actuated byelectrolyte under positive pressure from said path. t

7. The apparatus of claim 5 wherein said load-compensating means ishydraulic and includes piston means operable in cylinder means to definea pressure chamber communicating with said path upstream of said gap tobe actuated by electrolyte under positive pressure from said path.

8. The apparatus of claim 5 wherein said load-compensating meansincludes a separate hydraulic fluid-pressure system havingpressure-control means responsive to load reaction at said drive meansto maintain predetermined balance during gradual variations inelectrolyte pressure in said path.

9. The apparatus of claim 5 wherein said load-compensating means furtherincludes load control means comprising a pressure-sensitive transducerexposed to electrolyte pressure at a region upstream of said gap tosense sudden variations in electrolyte pressure in said path.

1. In electrolytic machining apparatus, mounting means for locating ashaping cathode in predetermined position with respect to a conductivemetal workpiece to define a gap therebetween; means for flowingelectrolyte between the cathode and the workpiece and through said gapunder positive pressure, the electrolyte pressure tending to producerelative retraction between the cathode and the workpiece, drive meansconnected to said mounting means for producing relative movement of thecathode toward the workpiece in the presence of the electrolytepressure; and load compensating means cooperating with said drive meansand separate and spaced from said mounting means for at least partiallyopposing said tendency to relative retraction and responsive to saidelectrolyte pressure, to be rendered inactive upon loss of saidelectrolyte pressure.
 2. In electrolytic machining apparatus, mountingmeans for locating a shaping cathode in predetermined position withrespect to a conductive metal workpiece to define a gap therebetween,means for flowing electrolyte between the cathode and the workpiece andthrough said gap under positive pressure; the electrolyte pressuretending to produce relative retraction between the cathode and theworkpiece; drive means for causing relative movement of the cathodetoward the workpiece along a path that determines the shaping of theworkpiece and in the presence of the electrolyte pressure;load-compensating means for providing opposing force to counteract atleast a portion of the force tending to cause relative retractionbetween the cathode and the workpiece; said load compensating meansbeing separate and spaced from said mounting means; and means connectedin load controlling relation to said compensating means directlyresponsive to electrolyte pressure between the cathode and the workpiecefor actuating said low compensating means in response to elevatedelectrolyte pressure and for relieving the load compensating means upona decrease in said electrolyte pressure.
 3. In electrolytic machiningapparatus, mounting means for locating a shaping cathode inpredetermined position with respect to a conductive metal workpiece todefine a gap therebetween; means for flowing electrolyte between thecathode and the workpiece and through said gap under positive pressure,the electrolyte pressure tending to produce relative retraction betweenthe cathode and the workpiece; drive means for moving the cathode towardthe workpiece in the pResence of the electrolyte pressure;load-compensating means for at least partially opposing said tendency torelative retraction between the cathode and the workpiece, and meansconnected in load-controlling relation to said compensating means anddirectly responsive to electrolyte pressure between the cathode and theworkpiece for rapidly relieving the load-compensating means upon asudden decrease in said electrolyte pressure.
 4. In electrolyticmachining apparatus, mounting means for locating a shaping cathode inpredetermined position with respect to a conductive metal workpiece todefine a gap therebetween; means for flowing electrolyte between thecathode and the workpiece and through said gap under positive pressure,the electrolyte pressure tending to produce relative retraction betweenthe cathode and the workpiece; drive means for producing relativemovement between the cathode and the workpiece in the presence of theelectrolyte pressure; load-compensating means responsive to saidtendency to relative retraction to at least partially oppose the same;said load-compensating means comprising at least one piston and cylindermechanism interposed between relatively movable elements of said drivemeans and means for directing pressured fluid to said cylinder.
 5. Inelectrolytic cavity-sinking apparatus, a hollow, electrically conductiveelectrode adapted to be advanced toward and into an electricallyconductive and electrochemically erodable workpiece to establish a workgap for flow of high-pressure electrolyte to support electrolyticcurrent flow between said workpiece and said electrode; means forestablishing an electrolyte flow path passing through said electrode andhaving said gap located intermediately therein; means for flowingelectrolyte under positive pressure through said path, the electrolytepressure between the cathode and workpiece tending to produce relativeretraction movement between the cathode and the workpiece; means forpassing low voltage, high-density direct current between the cathode andthe workpiece in a sense to make the workpiece anodic, and drive meansfor producing relative movement between the cathode and the workpiece inthe presence of the electrolyte pressure, the improvement ofload-compensating means for opposing reacting against said drive meansdue to electrolyte pressure along said path, said load-compensatingmeans being spaced from said electrode and connected to said drivemeans, said load-compensating means being directly responsive toelectrolyte pressure between the cathode and the workpiece and renderingthe load-compensating means inactive upon sudden escape of electrolytefrom said path at the region of said gap.
 6. The apparatus of claim 5wherein said load-compensating means is hydraulic and includes pistonmeans operable in cylinder means to define a pressure chambercommunicating with said path to be actuated by electrolyte underpositive pressure from said path.
 7. The apparatus of claim 5 whereinsaid load-compensating means is hydraulic and includes piston meansoperable in cylinder means to define a pressure chamber communicatingwith said path upstream of said gap to be actuated by electrolyte underpositive pressure from said path.
 8. The apparatus of claim 5 whereinsaid load-compensating means includes a separate hydraulicfluid-pressure system having pressure-control means responsive to loadreaction at said drive means to maintain predetermined balance duringgradual variations in electrolyte pressure in said path.
 9. Theapparatus of claim 5 wherein said load-compensating means furtherincludes load control means comprising a pressure-sensitive transducerexposed to electrolyte pressure at a region upstream of said gap tosense sudden variations in electrolyte pressure in said path.